First of all, congratulations for a spectacular implementation of these seemingly "conflicting" (at least in a non-destructive workflow) features.
Here, I got a fish-eye image where I want to paint the sky (say I want to make it darker). For the beginning, I just define the borderline between the earth and the sky.
Apply a lens correction and you get this:
Fantastic! The brush stroke got distorted almost perfectly. "Almost", because if you make a single brush click, painting a circle, it doesn't get distorted with lens corrections, turning into an ellipse (though the spot removal circles do). Instead all brush path point coordinates get recalculated along with the radius of the brush at each particular location. This works very well in real world even for extreme examples like de-fisheyeing. For rectilinear lenses, the difference is imperceptible.
And now, some bugs/limitations.
If you use a large brush, say I want to fill the whole sky in this example, things get a little more complicated.
Turn on lens corrections and...
The thick stroke gets distorted in a way that fill almost the entire image. This happens on extreme debarreling only. For normal lenses, it's a non-issue.
Also, sometimes I get a strange artifact in preview only. The exported image doesn't have this solid rectangle:
And a final, smaller, issue: for strong corrections like de-fisheye-ing, the brush pin easily gets lost outside the image area after you apply lens corrections.
Agreed, the Camera Raw team really have done a *fantastic* job with the new lens correction features, and I can't wait to use them in LR3 when it's released!
While we do the best we can mapping the local corrections, it is not perfect if you adjust the lens corrections after applying them, as you can see in some of your extreme examples.
In the future, when processing new images, if you apply the lens corrections first, and then the local corrections, you completely avoid these remapping issues.
Thomas, what about graduated filter and perspective corrections? It seems to be relatively easy to implement, since perspective corrections leave all the lines straight.